[x264-devel] Open GOP: problem with fixed pattern

[Thomas Mundt]

Hi,
I am trying to produce files that are as similar as possible to the Sony XAVC Long GOP encoders. To create the fixed GOP pattern IBBPBB...PBB with a GOP length of 24 frames, I used the following parameters:--keyint 24 --bframes 2 --b-adapt 0 --no-weightb --weightp 0 --open-gop --no-scenecut
Unfortunately, this only works from the second GOP onwards, tested with 1080p50, csp i422, 10 Bit input/output. The first GOP is only 22 frames long and sets a P-frame as the second frame. Perhaps this is due to the fact that an IDR frame is generated first, which according to the documentation contradicts an open GOP.However, the Sony encoder also generates an IDR frame first and then the two B frames.
Is it possible to get the x264 encoder to also generate the first GOP with the specified pattern (with IDR frame) and length?

Thomas
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